A turning insert is disclosed in U.S. Pat. No. 4,632,608. In turning of a metal work piece, the metal work piece rotates around a center axis. The metal work piece is clamped at one end by a chuck or jaws or by other means, which means rotates. The end of the work piece which is clamped can be called a clamping end or a driving end. For stable clamping, the clamping end or the driving end of the metal work piece has a larger diameter than the opposite end of the metal work piece and/or has a larger diameter of a portion of the metal work piece located between the clamping end and the opposite end. Alternatively, the metal work piece has a constant diameter before a machining, i.e. metal cutting, operation.
The turning insert is moved in relation to the metal work piece. This relative movement is called feed. The movement of the turning insert can be in a direction parallel to the center axis of the metal work piece, this is commonly called longitudinal feed or axial feed. The movement of turning insert can furthermore be in a direction perpendicular to the center axis of the metal work piece, this is commonly called radial feed or facing. Other angles of movement are also possible, this is commonly known as copying or copy-turning.
During the relative movement of the turning insert, material from the metal work piece is removed in the form of chips. The chips are can be short and/or have a shape or direction of movement which prevents chip jamming and/or do not give a poor surface finish of the machined surface.
A common shape of turning insert which can be used for a wide range of feed direction is the rhombic turning insert. Such insert has in a top view, i.e. the rake face towards the viewer, the shape of a rhombus. The two corners of the rhombus which are located at the greatest distance from each other forms nose cutting edges, which typically has a radius of curvature in the range of 0.2-2.0 mm. These two corners may have a nose angle of 55°. Examples of such turning inserts are commonly designated DNMG and DCMT according to ISO standard, and are commonly made at least partly from cemented carbide or cubic boron nitride (CBN) or ceramic or cermet.
Commonly in radial turning, the feed direction is towards the rotational axis of the metal work piece. Although radial turning away from the rotational axis of the metal work piece, also known as out-facing, in theory is advantageous when machining certain components, if common turning inserts such as DNMG or DCMT where to be used, poor chip control and fast insert wear would occur.
The turning insert in U.S. Pat. No. 4,632,608 is intended to overcome drawbacks in out-facing. The inserts have triangular and rhombic shapes, where the rhombic shape inserts comprise four nose portions, where two opposite nose portions are located at acute angles of the rhombus, including a cutting edge in the shape of a circular arc of an angle which is at least 180°. A portion of the circular arc shaped cutting edge is the only active cutting edge in out-facing. The turning insert in U.S. Pat. No. 4,632,608 can be used for machining two walls forming an external 90° corner in a metal work piece, where one wall is perpendicular to the rotational axis and one cylindrical wall is parallel to the rotational axis, where the two walls are connected by a circular segment.
Commonly in axial turning when machining the wall surface of an external 90° corner in a metal work piece which is parallel to the rotational axis of the metal work piece, the feed direction is towards the wall surface which is perpendicular to the rotational axis of the metal work piece. Also the turning inserts in U.S. Pat. No. 4,632,608 is used in this way.